That’s most likely caused by a low resolution heightmap or the transition between heights being too sharp. An image of your heightmap might help determine the issue.
Even if i zoom in a lot, the transitions arent too sharp. No idea what causes this 
If it’s a screenshot, then you the problem is that it doesn’t have a sufficiently high Bit-depth. Your screenshot is an 8 Bit image, which only gives you 256 individual steps of height. Heightmaps are usually stored as 16 Bit images, which have 65536 levels of height. No, there are no ways to just turn an 8 Bit image into a 16 Bit one, because it has too little information. Your best bet is the smoothing tool in Unreal (or get a proper heightmap image file).
this image is 32 bit
The question is whether it’s 32 Bit greyscale. 32 Bit may be RGBA with only 8 Bit per channel.
Yes it was a problem with 8 bit rgba, thanks